Improve and document record-cartfile-dependencies
Improve and document record-cartfile-dependencies

No longer requires a project name, and writes empty files for versions
without Cartfile dependencies.

jspahrsummers/Arbiter,ArbiterLib/Arbiter,jspahrsummers/Arbiter,ArbiterLib/Arbiter,jspahrsummers/Arbiter,jspahrsummers/Arbiter,ArbiterLib/Arbiter,ArbiterLib/Arbiter